1. Field of the Invention
The present invention relates to an image processing system suitable for character recognition of printed or handwritten characters such as those on slips.
2. Description of the Background Art
In a conventional character recognition of printed or handwritten characters on a tabular form slip in which characters are divided by ruled lines and blank spaces, at a time of image input, an optical filter treatment called drop out color is applied to remove a color constituting a form portion of the slip from the original image of the slip, so as to extract the characters to be recognized alone.
For this reason, in the conventional character recognition using the drop out color, it is impossible to deal with slips that use the form portion in colors other than those of the drop out color, or slips with a non-white background color. Moreover, it is also impossible to deal with multi-colored slips as well as the slips having characters in the color of the drop out color or in unspecified colors.
In order to resolve this problem, there has been a proposition for character recognition capable of dealing with slips by using the form portion in colors other than those of the drop out color, as disclosed in Japanese Patent Application Laid Open No. 61-15285 (1986), but this proposition relies on a technique for separating the characters from the character frames without separating the colors, so that it is only possible to realize a limited recognition level.
On the other hand, there are many propositions for character recognition which utilizes a technique of color separation for the input image. Examples of such conventional propositions includes those disclosed in Japanese Patent Application Laid Open No. 62-5485 (1987), Japanese Patent Application Laid Open No. 62-154181 (1987), Japanese Patent Application Laid Open No. 2-67689 (1990), Japanese Patent Application Laid Open No. 2-135584 (1990), Japanese Patent Application Laid Open No. 2-123488 (1990), Japanese Patent Application Laid Open No. 3-14077 (1991), Japanese Patent Application Laid Open No. 3-223987 (1991), Japanese Patent Application Laid Open No. 4-39789 (1992), Japanese Patent Application Laid Open No. 4-160486 (1992), and Japanese Patent Application Laid Open No. 4-354083 (1992).
However, in these conventional propositions, the accurate recognition of characters may not be possible when they are employed with relaxed constraints concerning the colors of the slips, the colors of the characters, the printing or handwriting method of the form portion and the characters, etc. for permitting a rough handwriting of the characters, for example. In addition, these conventional propositions have been unable to deal with a case involving color printing shear.
Furthermore, these conventional propositions merely propose the outlines for the character recognition schemes in which the color separation processing of some kind is applied to the colored input image to facilitate character recognition based on color separated image data as a replacement of character recognition using the drop out color, but fail to disclose any further detailed features necessary in constructing the practical character recognition system.
Thus, conventionally, a practically effective character recognition system not relying on the drop out color has been unavailable. For instance, there has been no practical scheme for handling a slip on which characters are printed in red over ruled lines printed in red and characters are printed in black over ruled lines printed in red are coexisting.